There are 40 students in a line. Rahul is 13th from the left and Kunal is 17th from the right. How many students are there between them?

Correct — C. Measure both boys from the same end before subtracting.

Rule: rank from the left = total − rank from the right + 1.

Kunal: 40 − 17 + 1 = 24th from the left
Rahul: 13th from the left
Between them: 24 − 13 − 1 = 10

That is option (c).

Why the others are wrong

• (a)
  7 — 7 between would put Kunal 13 + 7 + 1 = 21st from the left, which is 20th from the right. The stem puts him 17th from the right.
• (b)
  9 — 9 comes from taking Kunal as 40 − 17 = 23rd from the left, which drops the + 1. He is 24th, so the gap is 24 − 13 − 1 = 10.
• (d)
  12 — 12 between would put Kunal 13 + 12 + 1 = 26th from the left, which is 15th from the right, not 17th.

A ranking-in-a-row item gives two positions counted from opposite ends. They cannot be subtracted until both are measured from the same end.

Convert with total − rank + 1. The + 1 is there because the 17 counted from the right includes Kunal himself: 16 stand to his right, so 40 − 16 = 24 from the left.

With both ranks from the left, the number between is the larger minus the smaller, minus 1, because neither boy stands in the gap.

Key facts

• Rank from the left = total − rank from the right + 1.
• In a line of 40, the 17th from the right is the 24th from the left.
• The number strictly between ranks 13 and 24, counted from one end, is 24 − 13 − 1 = 10.

Common traps

• Converting 17th from the right to 40 − 17 = 23rd from the left, which drops the + 1 and gives 9.
• Subtracting 24 − 13 and stopping at 11, which counts one of the two boys as standing between.

No directly related past PYQ was found.